The present invention relates generally to articulated trucks and more particularly, to articulated trucks having a bed for carrying material therein.
Dump trucks have long been known in the art, for use in carrying different types of loads. One such use is in the construction industry for carrying dirt or other construction materials in the dump truck bed. A typical dump truck bed includes a tailgate defining a rear wall of the truck bed. The tailgate retains the material within the bed when the tailgate is in a storage or raised position and permits material to be ejected from the bed as the dump truck bed is raised. U.S. Pat. No. 5,456,521, assigned to the assignee of the present invention, discloses an unloading gate for a dump truck wherein the gate is mounted to one or more rails disposed on the bottom surface of the bed. The unloading gate moves from one end of the bed to the other to scrape and clean the bed after unloading or dumping of the material. The unloading gate in this patent is utilized in conjunction with a conventional dump truck bed which lifts at its forward end closest to the tractor cab and utilizes gravity to dump the material from the dump truck bed.
Applicant has had under development a new material carrying vehicle with a new material ejection system as is described in U.S. patent application Ser. No. 09/160,698, filed Sep. 25, 1998, now U.S. Pat. No. 6,155,776 entitled xe2x80x98Hydraulic System For a Work Machine Having an Ejector Cylinder and a Tailgate Cylinderxe2x80x99, assigned to the assignee of the present invention, which is hereby incorporated in its entirety herein. A variation of the above system is disclosed in U.S. patent application Ser. No. 08/936,128, filed Sep. 24, 1997, now abandoned entitled xe2x80x98Tailgate Latching Mechanismxe2x80x99, assigned to the assignee of the present invention, and hereby incorporated in its entirety herein.
Such a material eject system has a motor, for example, a hydraulic cylinder, that is connected to an ejector blade having a home position at the front end of the bed. To initiate a material eject operation, the motor moves the ejector blade toward the rear of the vehicle, thereby pushing the material in the bed off of the rear edge of the bed. The ejector blade is then retracted or returned to its home position at the front of the bed. The bed normally includes a tailgate which prevents material from exiting the bed while the material is being transported. During the material eject cycle, the tailgate is moved between its closed and open positions in synchronization with the operation of the ejector blade.
A vehicle having a material eject system has several advantages over traditional dump trucks. For example, the vehicle bed is not raised; and its center of gravity is not elevated as the material is being ejected. Therefore, vehicle stability is not adversely affected by the material ejection process. By maintaining a lower center of gravity, a material ejection system is more suitable for controlled spreading of the material during the ejection process. Further, by not raising the bed, the vehicle is not exposed to overhead obstacles such as trees and power lines. In addition, the profile of the ejector blade closely matches the cross-sectional profile of the bed and therefore, substantially all of the material in the bed is scraped out of the bed during the ejection process. Thus, a vehicle material ejection system is generally more efficient and flexible than the traditional elevating material dumping systems.
The motor driving the ejector blade is normally a hydraulic motor, for example, a multistage cylinder, that is supplied hydraulic fluid by a constant or fixed displacement pump being driven by the vehicle engine. Thus, the pump is supplying a fixed flow rate of fluid to the cylinder over the material eject cycle. The multistage cylinder is comprised of a plurality, for example, four nested telescoping cylinders of successively smaller diameters. During the material eject cycle, the hydraulic fluid is supplied to the largest cylinder segment which has the greatest volume. When that cylinder segment reaches the end of its stroke, the hydraulic fluid is supplied to a second smaller cylinder segment which has a smaller volume. Thus, the constant displacement pump will fill the second smaller cylinder segment in less time than it took to fill the first larger cylinder segment; and the second cylinder segment will extend at a faster speed than the first larger cylinder segment. That process continues with the extension of each successively smaller cylinder segment until the cylinder is fully extended. With each successively smaller cylinder segment, the smaller cylinder volume produces a greater speed of extension. Thus, as the ejector blade moves through the material eject cycle, the velocity of the ejector blade continuously increases. That increasing velocity of the ejector blade increases the rate at which material is ejected from the bed, thereby creating a nonuniformity in how the material is being spread as it is being ejected. Thus, there is a need to drive the ejector blade at a constant velocity throughout the material eject stroke in order to eject the material from the bed at a constant rate.
The present invention overcomes the foregoing and other shortcomings and drawbacks of material ejecting systems and methods of material ejecting heretofore known. While the invention will be described in connection with certain embodiments, it will be understood that the invention is not limited to these embodiments. On the contrary, the invention includes all alternatives, modifications and equivalents as may be included within the spirit and scope of the present invention.
In accordance with one embodiment of the present invention, a material eject system for ejecting material from a bed of a vehicle transporting the material has an ejector mounted to the bed of the vehicle which is movable between a forward end of the bed and a rear end of the bed. A motor is mechanically connected to the ejector and moves the ejector through an ejector stroke to dispense material from the bed. The motor, in response to a constant input, operates at a first speed during a first portion of the ejector stroke and operates at a second speed during a second portion of the ejector stroke. A speed control is operatively connected to the motor and automatically changes the input to the motor to operate the motor at the first speed during the second portion of the ejector stroke. Thus, by maintaining a constant motor speed, the ejector blade speed is moved at a constant velocity throughout the eject stroke and the layer depth of material being ejected is also constant.
Another embodiment of the invention is a method of a method of controlling an operation of a motor mechanically connected to an ejector operatively mounted on a bed of a vehicle. The bed contains material being transported by the vehicle. The method first moves the vehicle at a vehicle speed, and thereafter, simultaneously moves the ejector through an eject stroke at one of a plurality of selectable ejector speeds to eject the material from the bed of the moving vehicle and deposit the material in a layer.
The above and other objects, features and advantages of the present invention will become apparent from the following description and the attached drawings.